Lamp Repair

Discussion in 'The Projects Forum' started by LED Man, May 4, 2009.

  1. LED Man

    Thread Starter Active Member

    Jan 15, 2008
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    0
    Hey guys, I'm trying to repair a lamp and had some questions. I've attached a pic of the lamp and the pcb.

    Basically the wiper in the pot is busted and not making a clean connection, so the light goes on and off and from dim to really bright sporadically.

    So, it's either I replace the old pot on the board or I just design another board in place of the one already there. I'd like to design a new board in place of that one but don't really have experience designing a circuit.

    I assume there is a 12v 120ac signal coming which I input to the pot, but then it looks like there are 2 caps and a resistor in parallel with the pot? It also looks like a voltage regulator is on there? Or is that a transistor? The part number on it says BTA12 400C C514.

    Any help is appreciated, thanks guys.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    The BTA12 is a triac.
    The circuit used to dimm the lamp is probably a phase concrol circuit of some kind.
    I have attached the datasheet of the BTA12 and a PDF on the use of triacs.
    The PDF I have found on this page:
    http://www.educypedia.be/electronics/powerelectronicsdiac.htm

    Greetings,
    Bertus
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    I just read this a couple of days ago and found it interesting. No circuit design but a simple explanation of a dimmer switch...

    home.howstuffworks.com/dimmer-switch.htm

    S@H
     
  4. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Try cleaning the inside of the pot with contact cleaner, the lubricating kind.
     
  5. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Awesome thanks for all the info.

    Am I right in saying that the current circuit has an interference capacitor? I see one larger cap and one really small cap that is blue. I think I will redesign the circuit to incorporate the inductor choke because I remember noticing a significant buzz when the lamp was working. Also, I think I'm going to go off the circuit they have on this site http://home.howstuffworks.com/dimmer-switch4.htm. However I notice an extra resistor in the current circuit for the lamp, is that put in parallel to decrease the voltage drop?

    Also, is there anyway I can find and verify the right values for the components I'll need to buy? I know the triac but the caps I'm not sure. Also, is that long metal piece coming off the triac for heat dispersion? Not really sure what it's there for. Thanks guys.
     
  6. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Hey guys does this look about right for a circuit diagram of the dimming function? Thanks.
     
  7. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Is this diagram from the circuit you pulled out of the lamp?

    The diagram doesn't match the one from the website. If you take out the inductor, the Vin has three connections (CAP, RES, TRIAC) and the Vout has three connections (CAP, CAP, TRIAC). As far as component selection, I would try to identify the components on the current board and start there. I myself just went to the hardware store and bought another dimmer, so my experience ended with the website.
     
  8. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    I actually tried drawing up the schematic from the current board for the lamp.

    The other thing I guess I could do is just replace the pot. I'm not sure what type of pot it is and I don't have a DMM.

    Does anyone recognize what type of pot that is?
     
  9. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Is there anything written on the back side of it?
     
  10. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Nope, there is nothing written on the pot.

    Also, if I want to just replace the component, does anyone know of a way to remove solder without one of those solder suckers? All I have at the moment in a soldering iron. I feel like the easiest thing would just be to buy another pot and replace the one on there.
     
  11. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    You can get a copper braid that will wick up the solder after it is heated. It is sometimes referred to as Solder Wick or desoldering braid. It used to be available at Radio Shack.
     
  12. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Hey thanks. I actually was just able to remove it. Now I just need to find a replacement. There are no part numbers anywhere on the pot. Do you recognize it from the pics I posted? I can post some more pics of the pot if you want. Thanks.
     
  13. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Without any markings it is impossible to tell what resistance or power rating the pot is. Sorry.
     
  14. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like this schematic:

    [​IMG]

    In your drawing you have drawn 2 capacitors, I think one of them is the diac.
    Can you read the values of the capacitor?
    The RC time is max 1/2 cycle (8.33 mSec for 60 Hz and 10 mSec for 50 Hz).

    Greetings,
    Bertus
     
  16. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Thanks so much!
    The diac has a "30" on it.
    The cap looks like is says "333K 409V"
    The resistor is "Gold, Orange, Black, Brown"

    So I would basically input this circuit right in the positive AC main coming in?

    The ground wire is not interrupted at all throughout the lamp.

    Lastly, the inductor is right before the output to the bulb right? Thanks.
     
  17. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    The drawn coil is the load , in your case the lamp.
    The capacitor is 333K , that says 33 nF / 400 Volts.
    The resistor is "brown black orange gold" , that says 10 KOhm , 5 %
    The 30 on the diac is probably the trip voltage.

    The potmeter will probably be in the range of 250 KOhm.

    Greetings,
    Bertus
     
  18. LED Man

    Thread Starter Active Member

    Jan 15, 2008
    62
    0
    Hey guys, I know it's been a while but I just picked this up:
    http://www.radioshack.com/product/i...duxyeVQEwyZcBGg&productId=3012598&tab=support

    Do you think it will work? Also, I know terminals 2 and 3 are for the output of the pot, but what are the contacts for under the actual wiper? There are three contacts and not exactly sure what they are. In my previous posts on this thread I have a photo of the circuit board and there are inputs on the pcb that are perpendicular to each other. Now, I have to figure out how to input this new pot in the old terminal location. Thanks.
     
  19. bertus

    Administrator

    Apr 5, 2008
    15,648
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